A cellular base station typically consists of a radio equipment controller (REC) connected to one or more radio equipment (RE) units.
Generally these radios operate at the maximum transmit power levels. This is because RF multi carrier power amplifiers (PA) are designed to be most efficient at the maximum output power. When the PA is operated at lower transmitter output to save base station power, then the efficiency drops rapidly and the output becomes less linear.
Base station radio's power amplifiers typically use a Doherty design which is roughly 55%-65% efficient at the amplifier's optimal output. As the PA output is reduced, the overall power savings is much less than expected because of this reduced efficiency.
Base station radios can be designed to operate in one of multiple RF power classes. Power Class is a set of radio calibration parameters designed for an anticipated output power; such that when the radio is operating in that output power level this set of parameters do warrant a maximal power efficiency. Therefore each radio contains an array of power class to cover the expected operating range of the radio. This makes it possible to operate in low or high RF power output modes depending on the network coverage requirements. Low power modes are useful during off hour operation or in dense urban areas where cell site is small. High power modes are required for operation in rural areas or to support high bandwidth applications.
The base station radio's can be designed to operate in multiple RF output power classes for example 5, 10, 20, 40, and 80 watts. To achieve this, the radio's power amplifiers have to be re-configured to switch over the settings associated with each RF power class.
Currently base station radios switch power mode class by shutting off all the RF paths simultaneously as the RF power amplifiers are re-configured to operate at the new power class. This cut over induces a temporary outage thus is carefully managed especially during system operation. A power class change requires altering the power amplifiers' voltage bias to operate at the new transmit power level. The mobiles in this sector would see an abrupt outage and would start hunting for a new radio signal. This outage could last a number of seconds while the radio's power amplifier ramps up and the pre-distortion compensation is re-computed for the new output level.
Thus, on the one hand if a power amplifier is to remain in operation while reducing its power, the efficiency suffers drastically and the spurious RF emissions are increased. On the other hand, the amplifier's power class can be set lower to increase efficiency but this requires that the amplifier be shut off.
For these reasons, traditional power reduction implementations have limited capabilities in situations as described above.